1. Field of the Invention
The present invention relates to a paper feeding device provided for an image forming apparatus such as a copying machine or a printer.
2. Description of the Related Art
Conventionally, an image forming apparatus provided with an image forming section for forming an image on paper sheets, for example, a copying machine or a printer has been widely used. A paper containing section containing the paper sheets is attached to the main body of the image forming apparatus so that it can be pulled out. A paper feeding device for feeding the paper sheets in the paper containing section one at a time toward the image forming section is provided inside the main body of the image forming apparatus. The paper feeding device comprises a paper feeding roller for taking out the paper sheets in the paper containing section one at a time. A paper feeding roller which is approximately semicircular in cross section is most commonly used as the paper feeding roller.
The above described paper feeding device is so constructed that the driving of the paper feeding roller is forced to be stopped if a paper jam occurs in the position of the paper feeding roller. The occurrence of the paper jam is displayed on a display section so as to urge a user to perform paper jam processing. Consequently, the user recognizes that the paper jam occurs in the position of the paper feeding roller, to perform the paper jam processing. In this case, the paper jam processing is processing by pulling the paper containing section out of the main body of the image forming apparatus and removing the paper sheet which causes the paper jam to solve the paper jam state.
In the above described paper feeding device, however, the following problem arises if the paper jam occurs, after the paper feeding by the feeding roller has been started, in the position of the paper feeding roller in a state where a circular arc surface of the paper feeding roller nips the paper sheet in the paper containing section.
More specifically, if the paper feeding roller is stopped because the paper jam occurs in the above described state, the nip pressure of the paper feeding roller is applied to not only the paper sheet which causes the paper jam but also the paper sheets under the paper sheet, which have not been fed yet. In this state, if the paper containing section is pulled out of the main body of the image forming apparatus so as to perform the above described paper jam processing, not only the paper sheet which is jammed but also the paper sheets which have not been fed yet are wrinkled. Therefore, the wrinkled paper sheets which have not been fed yet must be taken out of the paper containing section and discarded. As a result, the paper jam processing becomes complicated, which takes long, and the paper sheets are wasted.
In order to deal with the above described problem, the applicant of the present application paid attention to the shape of the paper feeding roller. Specifically, the paper feeding roller which is approximately semicircular in cross section has a circular arc surface serving as a nip surface and a horizontal surface which does not nip a paper sheet. Accordingly, it is considered that when a paper jam occurs in the position of the paper feeding roller, paper sheets which have not been fed yet are not wrinkled at the time of paper jam processing if the rotation of the paper feeding roller is stopped not immediately but after returning the paper feeding roller to its home position where the nip surface is not opposed to the paper sheet and the horizontal surface is opposed to the paper sheet.
As a method of returning the paper feeding roller to the home position, a method of rotating the paper feeding roller in the reverse direction to return the paper feeding roller to the home position when the paper jam occurs in the position of the paper feeding roller is considered. In this method, however, a reversing mechanism for rotating the paper feeding roller in the reverse direction must be provided, although the paper sheets which have not been fed yet are not wrinkled at the time of the paper jam processing. Therefore, a mechanism for driving the paper feeding roller becomes complicated, and increased in size as well as manufacturing cost.